There is a need within the textile industry for pre-colored nylon yarns which can be combined with undyed nylon and then overdyed by a method which will color the undyed nylon without dyeing or staining the precolored nylon yarns. Such a precolored yarn may offer stylists an opportunity to achieve a wide variety of multicolored effects in carpeting and other textile applications which cannot be achieved in any other way. One way in which nylon producers have attempted to satisfy the need for precolored styling yarns is by a use of cationic dyeable nylon, one of two types of nylon, when considered from the standpoint of electrostatic charge.
Acid dyeable nylon is a synthetic long-chain polymer that includes a number of positively charged amine or amide groups that are receptive to negatively charged dyes. Among these anionic dyes are several categories, but the most important for use in dyeing acid dyeable nylon are the acid dyes and the premetallized acid dyes. Depending on the number of amine or amide groups in the acid dyeable nylon, it may be characterized as deep-dye, medium-dye or light-dye. Under certain conditions of temperature and pH level, acid dyes will form ionic bonds with the amine and/or amide groups in the nylon.
Cationic dyeable nylon is a type of nylon that has been treated by its manufacturer to impose an overall negative charge on the nylon. This makes it difficult for cationic dyeable nylon to accept negatively charged acid dyes at certain pH levels. Since most common liquids which may be spilled on carpet are negatively charged, cationic dyeable nylon therefore is naturally and inherently stain resistant.
Cationic dyeable nylon was initially developed to be dyeable with positively charged cationic dyes. When combined with acid dyeable nylon, unique multicolor effects may be created when acid dyes and cationic dyes are used in the same dyebath. However, cationic dyes do not generally offer the versatility and colorfastness properties of acid dyes, and so the use of cationic dyes to dye cationic dyeable nylon for styling purposes is somewhat limited.
Another way in which nylon producers have attempted to satisfy the need for precolored styling nylon has been by the use of color-sealed or solution-dyed nylon. These nylons are pigment colored during the extrusion process. This locks the color into the nylon structure, so it will not bleed during the overdye process. If solution-dyed nylon is cationic dyeable, it will not be stained by the acid dyes used to color the nylon in subsequent dyeing operations. However, solution-dyed nylon is only available in a limited number of pre-selected colors, which limits its usefulness as a styling tool.
In recent years, processes have been developed for dyeing cationic dyeable nylon with acid dyes and premetallized acid dyes. Such processes are described in U.S. Pat. No. 5,085,667 and U.S. Pat. No. 5,466,527 of Jenkins, U.S. Pat. No. 5,199,958 of Jenkins et al. and U.S. Pat. No. 5,626,632 of Boyes. These processes apparently involve the formation of ionic bonds between the acid and premetallized acid dyes and the fibers. Jenkins teaches the application of acid and premetallized acid dyes at pH levels within the range of about 2.0 to about 6.5 (4.0 to 6.5 in U.S. Pat. No. 5,199,958), and Boyes teaches the application of the same type of dyes at pH levels of 2.5 or below. However, while some of the shades produced by the methods of Jenkins and Boyes may sufficiently hold their color in continuous overdyeing, it is unlikely that shades produced by these methods will be substantive for extended periods of time when used to dye nylon in batch type overdye equipment such as a dyebeck, skein dye machine, package dyer, or paddle dyer.
U.S. Pat. No. 5,131,918 of Kelley teaches the application of a specific type of fiber reactive dyes to regular acid dyeable nylon that has been combined with cationic dyeable nylon. According to the Kelley method, the fiber reactive dyes are applied at a pH level within the range of about 2 to about 4, followed by steaming and washing, with the result that the acid dyeable nylon is dyed by the fiber reactive dyes while dyeing or staining of the cationic dyeable nylon is avoided.
Another method for dyeing acid dyeable nylon with vinyl sulfone type fiber reactive dyes was also developed by American Hoechst Corporation. According to this method, the vinyl sulfone dye was first pretreated with an alkali to convert the ester into the vinyl group, and then it was applied to acid dyeable nylon under moderate acid conditions. After washing, the printed nylon was dipped into an alkali solution, dried and heatset. When the vinyl sulfone dyes undergo heat setting under alkaline conditions, they form a covalent bond with the amine or amide groups of the nylon.
U.S. Pat. No. 5,445,653 of Hixson et al. describes a method for dyeing cationic dyeable nylon by application of fiber reactive dyes at a pH level no higher than 1.5. The nylon is steamed and washed to remove residual fiber reactive dyes and is then treated with an alkaline solution and heatset. During the heatsetting operation, the fiber reactive dyes form covalent or electron sharing bonds with the amine and amide groups in the cationic dyeable nylon, rather than the weaker ionic bonds of the methods of Jenkins and Boyes. The Hixson method, unlike the methods of Jenkins and Boyes, may be utilized to produce shades on cationic dyeable nylon that will be substantive when used to overdye the cationic dyeable nylon in combination with acid dyeable nylon in batch type overdye equipment such as a dyebeck, skein dye machine, package dyer, or paddle dyer. The inherent stain resistance of the cationic dyeable nylon resists dyeing and staining by acid dyes in the subsequent overdye operations and the covalently bonded fiber reactive dyes are extremely colorfast in dyebaths or continuous dye operations under ordinary overdyeing conditions.
U.S. Pat. No. 5,484,455 of Kelley also describes a method for dyeing cationic dyeable nylon with fiber reactive dyes. According to this method, a specific type of previnylized fiber reactive dye is applied to the nylon at pH levels between 1.5 and 3 (for printing) or between 2.0 and 3.0 (for exhaust dyeing). The nylon is then steamed and washed and an alkaline solution is applied in an amount necessary to raise the pH to between 9.0 and 10.5. After the alkane solution is applied, the nylon is dried and heatset to permit the formation of covalent bonds between the nylon and the dye.
Although both the Hixson method and the Kelley method of U.S. Pat. No. 5,484,455 appear to allow multicolored styling effects to be readily achievable, both methods also require heatsetting of the nylon in order to effect covalent bond formation. This may be done by autoclaving or in continuous wet or dry heat setting equipment such as Superba or Suessen ranges. Whatever method is used, heatsetting is an expensive and time-consuming operation. It would be desirable, therefore, if a method could be developed for dyeing cationic dyeable nylon with dyes capable of obtaining a wide range of colors without requiring a heatsetting step. It would also be desirable if such a method could be provided that would produce colored nylon capable of maintaining high colorfastness in dyebaths or continuous dye operations at 212.degree. F. It would also be desirable if such a method could be developed for dyeing cationic dyeable nylon in such fashion to resist dyeing and/or staining by acid dyes in subsequent overdye operations.